Abstract : A gyrotron traveling-wave device includes quarter wavelength anti-reflective dielectric layers to enhance microwave absorption. A drift tube made from a hollow waveguide is positioned within the gyrotron to surround an electron beam passing from an electron gun to a cavity. A plurality of parallel highly lossy dielectric suppressor rings are interspaced with a plurality of conductive rings positioned to surround the electron beam and located within the waveguide. An anti-reflective layer is formed on the suppressor rings of radiation due to parasitic oscillations by reducing reflections of incident radiation from the suppressor rings. In an alternate embodiment, one or more suppressor rings including an anti-reflecting layer are located within the cavity.